I must give a note to this old meditation I did. I've spent many years seeking and experimenting and seducing, working on reverse engineering the perfect method of rejuvination.
12 years in fact.
6 months prior to that 12 years, I discovered a way of meditation from a cliche book.

It had to do with laying down, letting go of all the bodies movement like you are dead.
Then moving feeling through the body.
Feel the foot, then feel the ankle, then feel the lower part of calf, then upper part, then feel the knee.

Now each time I would feel, I would stimulate with attention. Each time I would let go of the feeling.
Feeling is subtle tension.
Feel it, let it go. The is relaxation.
There are two forms of letting go/relaxation.
One makes the body heavier, one makes the body lighter.

Heavier is actually increased subtle stimulation in a relaxed manner. Like a dilating blood vessel, more blood yet relaxed. Lighter is true subtle relaxation. When the flesh is light the body feels good.

Anyway. There are two nerves in the body to release.
The spinal nerve and all its branches.
The vagus nerve and all its branches.

The subtle tension properly runs from the spine, from the spine the left side of it runs around to the middle of the body. The right runs around the right side to the center of the body.
This is the path of relaxation, you can focuse on the spine or front of body.

I advice taking the method, doing it for at least and hour before picking a spot and hyper focusing relaxation.
If you loose feeling of a spot, you have lost mental stimulation, an thus lost the ability to relax that spot.
Haha.

So. This is how you open the subtle body.
The body itself has a subtle state, released the gross mind and senses run through eachother easily.
For the gross, your mental capabilities and emotion range increase. Everything increases a bit.
Once your inner world was as stone, now it is filled with water. It can become as light as air, and fire is magic.
Fire = lighter than air, an updraft of force.

Anyway. This is the best way of opening the nerves that I know of.
Hour a day.
Hatha yoga uses too much tension in its methods. Proper hatha yoga actually attempts to use paresethesia.
Paresethesia: lower blood co2 levels.
Hatha yoga uses this breathing coupled with tension techniques. Although I suppose if correctly used, you would apply the tension technique, the stretch or bandah, an then you would relax. In the same way real taiji can utilize tension, and dark hado can utilize relaxation.

Anyway. A dedicated individual could become completely immortal in 1 year.
Rejuvination only takes 14 days to 30 to start.

I started with my entire nervous system closed.
Rejuvination doesn't need released subtle tension
When I was 15. An hour a day and 6 to 12 months and your entire nervous system will be open.
Want to be super about it? Do two hours.

The real issue is dedication.
Isolation of living is sought because those who are content and alone learn to relish in themselves. In having no physical human contact they only have themselves to reflect. In this they gain momentum.
I apologize for the ramble.

Oh yes. If you can pop your spine, it has subtle tension. This is am easy sign.

<snip>
Anyway. A dedicated individual could become completely immortal in 1 year.
Rejuvination only takes 14 days to 30 to start.

What you described is basically Shavasana (some its variation). It alone won't rejuvenate body. It is used mostly to train the body to relax before working with preparatory practices, such as Nadi Shodhana (series of classic breathing practices) to clean energy channels. Becoming good with Nadi Shodhana might take a couple of months, so it is a good time to also practice some classic Asanas (specifically Siddhasana). After that you are ready to start with initial Eastern practices. If you are serious about it, then be ready for lots of near-death-events on your path (with very high mortality factor) - that's one thing that noone speaks loud about. Good preparations lower the chance to die or get lost to illusions of your mind.

You are correct. This is nearly exactly what I was describing. I apologize if I lack clarity.
Shavasana will not rejuvenate the body. Although it can invigorate it.
Nadi Shodhana done correctly creates the condition for 'kundalini' as some call it.
Nadi Shodhana is a watered down practice meant to ease people into experience, this is why it takes months.

Nadi Shodhana is not very proficient in releasing the subtle body.

Nadi Shodhana is not very proficient in creating the condition for 'kundalini', this is because it is a technique given simply with little explanation.

Asanas are nearly useless for opening the nerves unless you can energize the nerves.

There is no need to fear death on the path.

Shavasana will not cause it. Nor will Nadi Shodhana.

Hell Nadi Shodhana will only create the condition for 'kundalini' if you practice it profusely. A slight adjustment can shorten this couple months down to 1 day. maybe a couple days if you have no experience in breathing practices.

The most dangerous practice is profuse pranayama. Yet there is no danger if it is kept to a medium level.

Becoming lost in the illusions of the mind. This happens constantly, it does not matter if you practice the internal art or not. I see many speak of spiritus mundi and magical effects of the moon. Yet reality is reality.
Even in the mental arts such as Samadhi and avishkara.
Avishkara would be the more dangerous practice. Without Samadhi it is illusionary. With Samadhi it is still delusional, yet the mind is a delusion. Samadhi simply allows you to fulfill a delusion. You can fake being an artist, or become the artist an thus produce art equal to the personality taken on.

If you are having near death experiences and many of them, this is due to your own situation. karma.
A lack of foresight coupled with clearing karma can lead to many undesirable situations. Even those with teachers rarely listen to the foresight of the teacher.

IF you have caused psychosis in yourself the diagnosis is variable.
When I first released the majority of my subtle body, I could feel all things. It took me a year to adjust. Even then, I do not use it full power.
In short, done correctly practice does not make you crazy.
I dish out the passive subtle method of releasing the psychic system.
Eastern practice is more forceful.
If the body psychic system is clear, then unintentional madness is rare. Diety yoga as its called, is a form of avishkara, which indeed can cause madness. Diety yoga and avishkara being the path of spirits.

This specifically is why mantra is taught. Mantra is a long soft approach.
Tulpa in Buddhism, avishkara in the yogas. This is manipulation of identity. For identity is a self ingrained delusion. This is the part that can cause madness.

Although I suppose releasing the subtle body can also cause such crisis in a person, as anyone not ready for it will experience extreme changes as their mental and emotional capacity expands past what they even knew was possible.

Nadi Shodhana is not very proficient in creating the condition for 'kundalini', this is because it is a technique given simply with little explanation.
<snip>
Hell Nadi Shodhana will only create the condition for 'kundalini' if you practice it profusely. A slight adjustment can shorten this couple months down to 1 day. maybe a couple days if you have no experience in breathing practices.

Nadi Shodhana doesn't have its goal to provoke Kundalini's movement, it is just to clear and balance Ida and Pingala. it is interesting to see the adjustments made for that practice, which allows to cut the work down to 1 day. I know, each school and teacher have their own approaches to these practices, and some of them aren't as good as the others.

Is this so?
XD
I thought that was the point of the practice!
= P Woops. Haha.
Clearing ida and pingala is much more difficult than I think it is made out to be.
Summoning prana will of course always quicken the practice of clearing.

Yet 'balancing' is a key factor in summoning kundalini.
You see the body itself does not work on a balanced system. It works on a counter balance system. Meaning by nature it is unbalanced.
Nadi shodhana if working traditionally brings equal pressured breathing in both nostrils. Meaning there is equal pressure in the carotid arteries.
(=
The condition of kundalini.
The second being a slight trance state.
I have no school nor teacher.